1. Field of the Invention
This invention relates to the field of polysaccharide hydrolysis and, in particular, it relates to methods and compositions useful for the partial hydrolysis (including hydration) of polysaccharides and to the complete hydrolysis of polysaccharides to form monosaccharides.
2. Description of the Art
The uses for partially and completely hydrolyzed polysaccharides are many and various. Sugars (primarily mono- and disaccharides) are used as foods and in foods for sweetening and food value, for the manufacture of syrups, confectioneries, preserves, etc.; as demulcents and lenitives; in the manufacture of soaps, pharmaceutical products, chemical intermediates for detergents, emulsifying agents, plasticizers, resins, explosives, glues, insecticides, and other products. One use for sugars, which is of current importance, is in their conversion by chemical or enzymatic processes to alcohols which are useful as fuels and fuel additives and in the manufacture of plastics, synthetic rubber, pharmaceuticals, and other chemical products. Partially hydrolyzed polysaccharides, including hydrated polysaccharides such as hydrated cellulose, are also useful in a variety of applications including the manufacture of glycogen, processed starch, and as chemical precursers for the manufacture of paper, fibers (including vulcanized fibers, mercerized cotton, and viscose rayon), and others.
While millions of pounds of various sugars (principally mono- and disaccharides such as glucose, sucrose, fructose, and maltose) are produced annually, most lower molecular weight mono- and polysaccharides, such as the sugars, are chemically bound into high molecular weight polysaccharides such as carbohydrates and animal and plant starches. By far the most abundant polysaccharide is cellulose which is the basic building block of all vegetable matter, and which is grown, harvested, and disposed of in immense quantities. Approximately 900 million metric tons of cellulose wasate (including discarded paper, crop stubbles such as corn stalks, rice stubble, etc., and sawdust) are produced in the United States each year. An immerse quantity of potential energy in the form of glucose is locked into this cellulose waste, and the great advantage to be gained by releasing that energy in the form of glucose has not gone unnoticed.
Several methods have been suggested for hydrolyzing higher molecular weight polysaccharides, such as cellulose, to their partially or completely hydrolyzed subunits such as glucose, and several are practiced commercially. For instance, it is known that polysaccharides, such as cellulose, can be hydrolyzed by the action of a strong base such as sodium hydroxide and calcium hydroxide. However, reaction rates are very slow, particularly at lower temperatures. Thus, economic production of base-hydrolyzed polysaccharides requires long contact times, high caustic concentrations (and cost) and relatively high temperatures on the other of 300.degree. F. (which requires the use of pressurized treating vessels). Furthermore, base is consumed in such processes in amounts proportionate to the amount of product obtained. A variety of bacterial and enzymatic processes also is known. For instance, it is known that papyan enzyme, if present in sufficient quantities, will gradually hydrolyze cellulose to glucose. It is also known that certain bacteria, such as Thermomonospora, which contain cellulase enzyme can convert cellulose to glucose for use by the bacteria, and that the cellulase enzyme, if isolated, might be employed to obtain glucose from cellulose. It is also known that the severe hydrolysis of polysaccharides, such as cellulose, with strong mineral acids, such as sulfuric acid, can be controlled to yield some glucose. However, dehydration and oxidation side reactions decrease the yield of glucose or other saccharide from the polysaccharide feed and consume the hydrolyzing agent, e.g., sulfuric acid, as illustrated in the following expression: EQU [C.sub.6 H.sub.10 O.sub.5 ].sub.n +2nH.sub.2 SO.sub.4 .fwdarw.n[5C+CO.sub.2 +2SO.sub.2 +7H.sub.2 O].
Accordingly, a significant need exists for improved processes for partially or completely hydrolyzing polysaccharides to form hydrated polysaccharides, lower molecular weight polysaccharides, and/or monosaccharides.
It is therefore one object of this invention to provide improved methods and compositions for hydrolyzing polysaccharides.
Another object is the provision of methods and compositions for producing lower molecular weight polysaccharides from higher molecular weight polysaccharides.
Another object of this invention is the provision of methods and compositions useful for converting polysaccharides to monosaccharides.
Yet another object is the provision of methods and compositions useful for converting cellulose to hydrated cellulose.
Another object is the provision of methods and compositions useful for converting cellulose to glucose.
Other objects, aspects, and advantages of this invention will be apparent to one skilled in the art in view of the following disclosure and the appended claims.